The present application is based on and claims priority from Japanese Patent Application Hei 10-322102 filed Nov. 12, 1998, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a commutator of a rotary electric machine such as a dc motor and a method of manufacturing the same and, particularly, a commutator segment.
2. Description of the Related Art
There are the following two types of commutators of electric motors according to rotation speed and other operating conditions of the motor: an assembled type commutator; and a mold type commutator. The assembled type commutator is an assembly of a plurality of commutator segments formed separately, an insulation body, and an annular insulation member. On the other hand, the mold type commutator is a mold unit of a cylindrical conductor member and an insulation body made of thermo-setting resin, which is machined to divide the cylindrical conductor member into commutator segments.
In a conventional mold type commutator, each commutator segment has a pair of inner claws at the inner surface thereof extending axially and radially inward to be secured to the insulation body. However, such a pair of inner claws is not sufficient to secure the commutator segment to the insulation body under severe operation conditions such as a high centrifugal force, a high rotation speed, and/or high tensile force. In manufacturing such a mold type commutator, a insulation body is molded with a cylindrical conductor member and machined, and commutator segments are cut out from the cylindrical conductor member. During such machining or cutting process, the outer periphery of the commutator segments may not form smooth surface because of thermal expansion or contraction.
A main object of the invention is to provide an improved commutator of a motor that is inexpensive and reliable.
Another object of the invention is to provide a reliable mold type commutator having an insulation body and a plurality of commutator segments which are tightly secured to the insulation body.
According to a preferred embodiment of the invention, a commutator of an electric motor includes a plurality of commutator segments and a cylindrical insulation body anchoring the plurality of commutator segments at the outer periphery thereof. Each of the commutator segments has a pair of wedge portions as well as a pair of inner claws. The pair of wedge portions is disposed axially outside and a circumferential side of each of said pair of inner claws so that each of the commutator segments holds the insulation body by both the pair of inner claws and the pair of wedge portions.
Therefore, the commutator segments and the insulation body are tightly bonded to each other over the entire length thereof and form a durable commutator operable under severe operation conditions such as a high centrifugal force, a high rotation speed, and/or high tensile force. Moreover, ribs are formed to maintain the distance between the adjacent wedge portions, thereby maintaining smooth surface after machining or cutting process. Dovetail portions are preferably formed at the edges of the wedge portions to increase resistance against thermal expansion or contraction of the insulation body. This prevents a brush noise and abnormal commutation caused by uneven surface of the commutator. Further, the inner claws, the wedge portions, the dovetail portions and ribs can be formed simultaneously by punches at a low cost.